The London Fire Brigade and London Ambulance Service went to the scene, and roads were closed around the incident.

London Fire Brigade told The Metro two people were taken to hospital and 13 more were treated at the scene.

Sam Kazmanli, the station manager, said: "The building has been severely damaged so a cordon has been put in place and people have been evacuated from the area.

"Firefighters worked quickly to ensure there were no additional casualties. I’d ask people to avoid the area if possible as there is heavy traffic disruption."

A London Ambulance Service spokesman said to PA: "We treated 17 patients at the scene. We took three patients as a priority to hospital.

"A further nine adults and four children with minor injuries were also taken to hospital and one was treated and discharged at the scene."

The Metropolitan Police said no-one had suffered life-threatening injuries, while Transport for London (TfL) announced a full investigation would be launched into the incident.

Tony Akers, TfL's head of bus operations, said: "At around 2pm on Sunday 15 May, a route 18 double deck bus, operated by Metroline, was involved in a collision with a building on High Street Harlesden near the junction with Wendover Road, NW10.

"Emergency services attended the scene. There will be a full investigation into the incident."